This apparatus is directed to an opacity transmitter. It is particularly constructed and arranged for installation with an oil mist generator. An oil mist generator is a device which forms a mist of lubricating oil to be supplied to rotating machinery for lubrication purposes. While other applications can be imagined, this apparatus will be described in the context of an oil mist generator. The mist is delivered through a suitable conduit. As a convenience, a pipe having a two inch ID is suggested, and delivers the mist of oil from a suitable source to a rotating machine requiring such lubrication. If lubrication were to fail, catastrophic failure may follow soon thereafter. The oil misting lubrication system is preferably monitored. This enables the formation of an alarm signal indicative of oil mist failure, thereby providing adequate early warning so that the oil misting apparatus can be checked or the rotating machinery shut down until repairs are made.
Since oil mist monitors are frequently used in an explosive environment, it is desirable to comport with industrial standards for explosion proof equipment. The opacity transmitter therefore employs an electrically insulative case having no lens or windows and its circuitry, operated from a remote power supply in a safe location, is designed to limit maximum current draw to a safe level in the event that a short might occur. Further, certain electrical inspection may be accomplished externally with the transmitter housing in its closed and sealed condition. The oil mist monitor is thus intrinsically safe for use even in areas having an explosive atmosphere.
Typically, the oil mist is formed by a device for this purpose and is delivered through a pipe. As an example for the present disclosure, the pipe is assumed to have a two inch ID whereby a continual flow of air borne oil droplets is delivered to rotating machinery. This apparatus is best installed in the pipe delivering the oil mist to the rotating machinery. A location can be obtained by cutting the pipe, removing a portion thereof, and installing the present invention. It lends itself to easy installation because it is preferably constructed with a pipe cross having four legs at right angles. Two of the legs are located to continue the flow and they are therefore connected in the oil mist delivery system. Two tubular legs are provided at right angled position to the flow path. Within these legs is located the measuring apparatus of this disclosure. The apparatus is typically installed with the opposing tubular legs positioned horizontally to avoid creating a trap in either leg which might permit settling of the droplets to obscure operation of the equipment.
With the foregoing in view, this apparatus is briefly summarized as providing a pipe cross utilizing transverse arms to locate light emitting diodes (LEDs) at one end transmitting light across the oil mist flow path to photo cells at opposite end of the cross. The apparatus provides LED responsive electrical circuitry representing an opacity transmitter which measures the light absorbence of a sample and outputs a direct current signal at a suitable current range, such as from 4 ma to 20 ma, which is inversely proportional to the percent transmission of the signal. The instrument functions as a conventional 4-20 ma transmitter with the current through the reference LED plus the current through the LED array source together with the current needed by the amplifier totals 4 ma at zero absorbence or 100% transmission and 20 ma at full scale. This relationship determines the value of individual currents for a given range of transmission for the two path lengths of the measure and reference light sources. A suitable reference LED and a photo cell are included in the circuitry. The two photo cells form a matched pair with the reference photo cell operating a differential amplifier and forming a reference signal which is indicative of a predetermined condition of oil mist opacity, this being indicated by absorption units or percentage transmission through the oil mist in the light detected by the reference cell. The LED light is at a wavelength which renders the oil transparent so that an oil coating on the light source and detector does not change the output. Light scatter from oil droplets in the sample cause attenuation of the signal.